A quarter of the British population will experience some kind of mental health problem in the course of a year, with mixed anxiety and depression the most common mental disorder in the UK. Depression affects an estimated 350 million people around the world, fewer than half of those affected receive treatment. In some countries, the figure is fewer than 10% due to barriers of health resources, a lack of healthcare workers and social stigma.

On Depression Awareness Week, organised by the charity Depression Alliance, we look at facts about one of the most common illnesses.

Depression is different from usual moon fluctuations and short-lived emotional responses to challenges in everyday life. Particularly when long-lasting with moderate to severe intensity, depression is a serious health condition, and at its worst, can lead to suicide.

An estimated one million deaths are caused by depression-related suicide every year. Suicide rates show that British men are three times as likely to die by suicide than British women.

Self-harming statistics for the UK show one of the highest rates in Europe, with around 400 per 100,000 population.

Women are more likely to have been treated for a mental health problem than men and about 10% of children have a mental health problem at any one time.

One in 10 children between the ages of one and 15 has a mental health disorder.

Only one in 10 prisoners has no mental disorder.

Male prisoners are 14 times more likely to have two or more disorders than men in general, and female prisoners are 35 times more likely than women in general.

Even in some high-income countries, people who are depressed are not always correctly diagnosed. Others who do not have the disorder are occasionally misdiagnosed and prescribed antidepressants.

Depression affects one in five older people living in the community and two in five living in care homes.

What are the symptoms of depression?

Depression has a variety of different physical and mental symptoms, some of which include lasting feelings of hopelessness and sadness, losing interest in things you used to enjoy, thoughts of self-harm or suicide and anxiety. Physical symptoms include tiredness, sleeping badly, having no appetite or sex drive and experiencing various aches and pains.

Rather than normal spells of feeling down, depression can lead to the patient feeling persistently sad for weeks, months or years. Although depression is a dangerous illness, the right treatment and support can help facilitate a full recovery. It is important to seek help from your GP if you think you may be depressed.